Comparison of metastatic phenotypes in mammary tumours of the dog and cat.

Forty-eight canine and 57 feline mammary carcinomas with the corresponding lymph node metastasis were available for immunohistochemical analysis using a panel of antibodies (anti-ER, -PR, c-erbB-2, -P63, -CK14, -CK5/6, -CK19). The tumours and metastases were classified, according to a standardized algorithm, into one of the following 5 phenotypes, namely Luminal A and B; non-luminal: c-erbB-2 over-expressing, basal-like, normal-like. Canine primary tumour phenotypes evidenced a higher prevalence of luminal carcinomas (30/48) (P<0.05) while the cat showed a majority of c-erbB-2 over-expressing (22/57) (P<0.05). In lymph node metastases a significantly higher frequency of non-luminal phenotypes was evidenced in both species (P<0.01). In the dog, the basal-like (18/48) type was prevalent followed by the c-erbB-2 over-expressing (14/48) type, while in the cat the c-erbB-2 over-expressing (27/57) prevailed followed by the basal-like (17/57) type. This investigation confirms that the main difference between mammary canine and feline carcinomas concerns the hormone receptor expression, which is higher in canine primary tumours. In both species when the initial site of metastasis is considered (regional lymph node) there is a shift from hormone positive to hormone negative phenotypes.